There I was, at the physiotherapist, reading a new manuscript by a friend and collaborator to distract myself from the indignities being visiting on my calf. There I was, thoroughly enjoying what I was learning, when I was brought up short by a construction that drives me up the wall:

“this species, therefore, cannot be not congeneric with A. jonesi. Instead, it actually belongs to Ethereum, a similar but unrelated genus”.*

I gasped. Unrelated? No two genera on Earth are “unrelated”. There are closely related genera and distantly related ones, but because all life on Earth shares a common ancestor, there are no unrelated ones.

Of course, I understood that my friend meant “distantly related”, and I’ll even grant you that every single person who read the paper would understand it that way too. That’s probably why I come across “unrelated” so frequently – even, I have to admit, sometimes in my own writing. So if you think that among things people get wrong in writing, this one is decidedly trivial, I really can’t argue with you.

It’s still on my “pet peeves” list, though, and here’s why. The fact life on Earth had a single origin – with every living species descended from just one common ancestor – is the single most mindblowing thing biology has ever discovered. One origin, one ancestor, and from that one ancestor natural selection has given us penguins and pangolins and protozoa and plantains. How could we ever offer anyone, even for a moment, a chance to forget that?

The incredible power of natural selection and the common ancestry of modern species are, of course, key pieces of Darwin’s argument in The Origin of Species – the most important work ever published in biology. And yet in his concluding sentence, Darwin hedged on whether all life had a single origin:

There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved (Darwin 1859; emphasis added)**.

I’m not enough of a Darwin scholar to know why he hedged, but perhaps he knew he was already giving people a lot to chew on. In any event, the single origin of life is now inextricably bound to Darwin’s insight. It will stay the most mindblowing thing in biology – unless and until we discover an independent origin of life elsewhere in the universe. Europa?TRAPPIST-1g? Gliese 667 Cc? A discovery of life that doesn’t share a common ancestor with all of us on Earth would be the most exciting thing I can imagine happening to biology.

And it would let me remove “an unrelated genus” from my list of Writing Pet Peeves.

I always thought Darwin was just being a good scientist and refusing to speculate when he knew he didn’t have a complete picture. What’s cool is how radically the tree of life has changed since I finished grad school in 1985, and your paragraph about how we’re all related is still true.

Teaching Biology to monks in Tibet, they had the most wonderful thought, completely novel to me although potentially obvious if you actually study the origin of life: How do we know that the first cell was the first cell? How do we know that there weren’t cells before that just didn’t make it? That the origin of life is actually not the ‘first’ but merely the first to have successful descendants. For some reason I had never thought about it, and it was mind-blowing. But I love your pet peeve!

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